The present invention relates to testing cell phones in a lab that simulates environmental conditions. In particular, it relates to new testing capabilities for simulating changes in correlation characteristics of signal components delivered to a cell phone. Correlation characteristics express changing environmental conditions and physical relationships among antennas in the cell phone and at base stations.
New cell phone designs require testing, especially as new network features and designs are introduced. Network operators, phone manufacturers and others need test equipment to assure that new phone models function smoothly.
The so-called long-term evolution (LTE) of cellular networks from third to fourth generation technology presents new challenges for testing. An overview of testing approaches to LTE can be found in M. Rumney, ed., LTE and the Evolution to 4G Wireless, Chapters 6-7 at 199-426 (Wiley 2009). As comprehensive as this discussion is, the topic of multipathing is not even listed in the index to the book.
The evolutionary plan calls for cell phones and base stations each to have multiple antennas. Processors in the phones and base stations will sense the phase difference between antennas and adjust their signal processing to take into account the physical relationship among the antennas at each end. At various cellular frequencies, the wavelength may be more or less than 1 foot. Significant phase differences can easily exist with such short wavelengths.
Standards have developed for cell phones with incoming signals that have testing phase differences, especially for types of multipathing encountered in different environments. Standards preparation efforts related to testing that extend to multipathing include 3GPP's so-called Spatial Channel Models (at www.3gpp.org) and the European Information Society Technologies' (“IST”) WINNER project (at www.ist-winner.org). We collectively refer to these efforts to describe operating environments as propagation channel models (“PCMs”). Referring to environmental conditions as propagation channel models allows us to refer to and explain classic channel models and spatial channel models without confusion between environments that are being modeled and the mathematics used by the model.
The standard multipathing environments do not attempt to model the dynamics of a person turning their head as they talk or of driving on the freeway or moving from one environment to another during a call. One approach to the person turning their head test is to mount a cell phone in RF chamber attached to a robot that moves the cell phone and simulated body parts, a hand and head. Approaches to so-called drive testing include fading the signal and actually driving with an instrumented cell phone. Testing approaches have yet to develop for the corner case of a cell phone moving from one environment to another during a call. Existing test protocols are not adequate to fully test the next generation of phones and networks.
An opportunity arises to introduce improved test equipment that handles scenarios which did not arise with prior generations of cell phones and networks or that were inadequately tested.